Rationale and efficacy of proteasome inhibitor combined with arsenic trioxide in the treatment of acute promyelocytic leukemia

Ablation of Wnt signaling in bone marrow stromal cells overcomes microenvironment-mediated drug resistance in acute myeloid leukemia

The survival of leukemic cells is significantly influenced by the bone marrow microenvironment, where stromal cells play a crucial role. While there has been substantial progress in understanding the mechanisms and pathways involved in this crosstalk, limited data exist regarding the impact of leukemic cells on bone marrow stromal cells and their potential role in drug resistance. In this study, we identify that leukemic cells prime bone marrow stromal cells towards osteoblast lineage and promote drug resistance. This biased differentiation of stroma is accompanied by dysregulation of the canonical Wnt signaling pathway. Inhibition of Wnt signaling in stroma reversed the drug resistance in leukemic cells, which was further validated in leukemic mice models. This study evaluates the critical role of leukemic cells in establishing a drug-resistant niche by influencing the bone marrow stromal cells. Additionally, it highlights the potential of targeting Wnt signaling in the stroma by repurposing an anthelmintic drug to overcome the microenvironment-mediated drug resistance.

Pyrrolidine Dithiocarbamate Enhances the Cytotoxic Effect of Arsenic Trioxide on Acute Promyelocytic Leukemia Cells

BACKGROUND

More than 95% patients with acute promyelocytic leukemia (APL) carry the PML-RARα fusion oncoprotein. Arsenic trioxide (ATO) is an efficacious therapeutic agent for APL, and the mechanism involves the binding with PML and degradation of PML-RARα protein. Pyrrolidine dithiocarbamate (PDTC) demonstrates the function of facilitating the cytotoxic effect of ATO.

PURPOSE

To investigate whether PDTC is potential to enhance the cytotoxic effect of ATO to APL cells by acting on PML-RARα oncoproteins.

METHODS

Inhibitory effects of drugs on cell viability were examined by CCK-8 test, and apoptosis was evaluated by flow cytometry. Western blotting and immunofluorescence assays were used to explore the mechanism.

RESULTS

PDTC improved the effect of ATO on inhibiting proliferation of NB4 cells in vitro. Further, PDTC-ATO promoted apoptosis and cell cycle arrest in NB4 cells. The expression of caspase- 3 and Bcl-2 was reduced in PDTC-ATO-treated NB4 cells, while cleaved caspase-3 and Bax was up-regulated. Furthermore, less PML-RARα expression were found in PDTC-ATO-treated NB4 cells than that in NB4 cells treated with ATO singly. Laser confocal microscopy showed that protein colocalization of PML and RARα was disrupted more significantly by PDTC-ATO treatment than that with ATO monotherapy.

CONCLUSION

In conclusion, PDTC enhanced the cytotoxic effect of ATO on APL, and the mechanism was, at least in part, related to the promotion of ATO-induced degradation of PML-RARα fusion protein via forming a complex PDTC-ATO.

1,3-Benzodioxole Derivatives Improve the Anti-Tumor Efficiency of Arsenicals

Arsenicals have been widely used in the treatment of cancers such as leukemia and other tumors. However, their side effects limit their clinical application. Stiripentol, a second-line adjunctive treatment for epilepsy with a good safety profile, inhibits microsomal cytochrome-P450-family enzymes to extend the retention time of co-administration. Inspired by the metabolism of stiripentol, the 1,3-benzodioxole responsible for the inhibition and its metabolic derivatives were conjugated with arsenical precursors. The fabricated arsenicals were eliminated much slower in mice and maintained an efficient concentration in the blood for a longer time than that of the arsenical precursors. They also performed better in anti-proliferation by inhibiting the thioredoxin system to induce oxidative stress, and concomitantly to initiate apoptosis in vitro and in vivo. The fabricated arsenicals reversed the hemogram of tumor-bearing mice to normal and eliminated the tumor without causing damage to any organs, exhibiting a good design strategy and pre-clinical application for leukemia and other tumors.

Microenvironment and drug resistance in acute myeloid leukemia: Do we know enough?

Acute myeloid leukemia (AMLs), as the name suggests, often develop suddenly and are very progressive forms of cancer. Unlike in acute promyelocytic leukemia, a subtype of AML, the outcomes in most other AMLs remain poor. This is mainly attributed to the acquired drug resistance and lack of targeted therapy. Different studies across laboratories suggest that the cellular mechanisms to impart therapy resistance are often very dynamic and should be identified in a context-specific manner. Our review highlights the progress made so far in identifying the different cellular mechanisms of mutation-independent therapy resistance in AML. It reiterates that for more effective outcomes cancer therapies should acquire a more tailored approach where the protective interactions between the cancer cells and their niches are identified and targeted.

Prediction of Essential Genes in Comparison States Using Machine Learning

Identifying essential genes in comparison states (EGS) is vital to understanding cell differentiation, performing drug discovery, and identifying disease causes. Here, we present a machine learning method termed Prediction of Essential Genes in Comparison States (PreEGS). To capture the alteration of the network in comparison states, PreEGS extracts topological and gene expression features of each gene in a five-dimensional vector. PreEGS also recruits a positive sample expansion method to address the problem of unbalanced positive and negative samples, which is often encountered in practical applications. Different classifiers are applied to the simulated datasets, and the PreEGS based on the random forests model (PreEGSRF) was chosen for optimal performance. PreEGSRF was then compared with six other methods, including three machine learning methods, to predict EGS in a specific state. On real datasets with four gene regulatory networks, PreEGSRF predicted five essential genes related to leukemia and five enriched KEGG pathways. Four of the predicted essential genes and all predicted pathways were consistent with previous studies and highly correlated with leukemia. With high prediction accuracy and generalization ability, PreEGSRF is broadly applicable for the discovery of disease-causing genes, driver genes for cell fate decisions, and complex biomarkers of biological systems.

Arsenic compounds: The wide application and mechanisms applied in acute promyelocytic leukemia and carcinogenic toxicology

Arsenic (As), as well as its various compounds have been widely used for nearly 4000 years either as drugs or poisons. These compounds are valuable in the treatment of various diseases ranging from dermatosis to cancer, thereby emphasizing their important roles as therapeutic agents. The ability of As compounds, especially arsenic trioxide (ATO) in the treatment of acute promyelocytic leukemia (APL), has fundamentally altered people's understanding of the poison, and has become a major factor in the re-emergence of Western medicine candidates to treat leukemia and other solid tumors. However, long-term exposure to As has been correlated with numerous disadvantageous influences on health, particularly carcinogenesis. Importantly, accumulating evidence suggests that biotransformation of As, as a step to eliminate As from the human body, can induce alterations at the genetic and epigenetic levels, resulting in therapeutic effects or carcinogenesis. In this article, we aimed to provide a systematic overview of the primary contributions associated with As and its compounds, as well as the detailed mechanisms applied in APL cells and carcinogenic toxicology. This review may help to understand the underlying mechanisms and safe wide clinical applications of medicinal As along with its compounds.

Mitochondrial metabolism as a target for acute myeloid leukemia treatment

Acute myeloid leukemias (AML) are a group of aggressive hematologic malignancies resulting from acquired genetic mutations in hematopoietic stem cells that affect patients of all ages. Despite decades of research, standard chemotherapy still remains ineffective for some AML subtypes and is often inappropriate for older patients or those with comorbidities. Recently, a number of studies have identified unique mitochondrial alterations that lead to metabolic vulnerabilities in AML cells that may present viable treatment targets. These include mtDNA, dependency on oxidative phosphorylation, mitochondrial metabolism, and pro-survival signaling, as well as reactive oxygen species generation and mitochondrial dynamics. Moreover, some mitochondria-targeting chemotherapeutics and their combinations with other compounds have been FDA-approved for AML treatment. Here, we review recent studies that illuminate the effects of drugs and synergistic drug combinations that target diverse biomolecules and metabolic pathways related to mitochondria and their promise in experimental studies, clinical trials, and existing chemotherapeutic regimens.

Evolving Chemotherapy Free Regimens for Acute Promyelocytic Leukemia

With the treatment advances over the last three decades, acute promyelocytic leukemia (APL) has evolved from being the most malignant form of acute leukemia to a leukemia with excellent long term survival rates. In the present review, we have summarized data leading to the development of the currently used treatment regimens for APL, which incorporate either none or minimal chemotherapeutic drugs. We have discussed the historical aspects of APL treatment along with the challenges associated with chemotherapy-based approaches and our experience with the use of single agent arsenic trioxide (ATO) which was one of the first successful, non-chemotherapy approaches used for APL. Subsequently, we have reviewed the data from major clinical trials in low-intermediate risk APL and high risk APL which guide the current clinical practice in APL management. With accumulating data on oral ATO, we postulate that the treatment for low-intermediate risk APL will be a completely oral ATO + ATRA regimen in the future. While for high-risk APL, we believe that minimal anthracycline use with ATO + ATRA might become the standard of care soon. A number of promising non-chemotherapy drugs with pre-clinical data would merit clinical testing in the high risk and relapsed setting, with potential to translate to a complete oral chemotherapy free combination regimen in combination with ATO and ATRA.

Suppression of proteasome induces apoptosis in APL cells and increases chemo-sensitivity to arsenic trioxide: Proposing a perception in APL treatment

In the last three decades, the pathogenesis of acute promyelocytic leukemia (APL) has been mostly studied with regard to the oncogenic role of PML/RAR fusion protein; however, the latest discoveries have stated that the concerns with the treatment of APL patients would not be resolved until the role of aberrant networks is overlooked. The present study was designed to evaluate the anti-cancer property of second-generation of the proteasome inhibitors carfilzomib (CFZ) on APL-derived NB4 cells. Our results showed that pharmacologic targeting of proteasome in NB4 reduced the proliferative rate of malignant cells through a c-Myc-mediated G2/M cell cycle arrest. Moreover, we found that the suppression of proteasome was coupled with the induction of apoptotic NB4 cell death, which is probably mediated through down-regulation of anti-apoptotic target genes. Interestingly, our results suggested that the suppression of the autophagy system using chloroquine could serve as a mechanism through which the cytotoxicity of CFZ in APL cells was ameliorated. Finally, and consistent with the favorable efficacy of single agent of CFZ, we also noted an intensifying effect of the inhibitor on the anti-leukemic activity of arsenic trioxide (ATO) when it was used in combination. Overall, this study suggests that pharmaceutical targeting of proteasome using CFZ, either as a single agent or in combination with ATO, could be a promising mechanism through which the obstacle on the way of APL would be tackled; however, further investigations are needed to determine the advantages of the inhibitor in clinical applications.

Pyrrolidine Dithiocarbamate Facilitates Arsenic Trioxide Against Pancreatic Cancer via Perturbing Ubiquitin-Proteasome Pathway

Purpose

To investigate whether pyrrolidine dithiocarbamate (PDTC) could facilitate arsenic trioxide (ATO) to induce apoptosis in pancreatic cancer cells via perturbing ubiquitin-proteasome pathway.

Methods

Mass spectrometry was performed to examine the interaction between PDTC and ATO, and the data showed they could form a complex termed PDTC-ATO. Inhibiting effects on cell viability were examined by CCK-8 test, and apoptosis was examined by flow cytometry. Four treatment arms (n = 6), including the control, PDTC, ATO, and PDTC-ATO, were evaluated using BALB/c nude mouse models bearing a xenograft tumor of SW1990 human pancreatic cancer line. Western blot, immunohistochemistry assays were to detect the mechanism.

Results

The results showed that PDTC-ATO had higher inhibiting effects on proliferation of pancreatic cancer cells than ATO in vitro. In bearing-tumor mice, PDTC-ATO inhibited tumor growth by 79%, being more potent than ATO (by 46%) or PDTC (by 35%) compared to the control. Results of Western blot and immunohistochemistry showed proteasome inhibition and apoptotic cell death, together with obvious suppression of associating E3 ubiquitin ligase activity, occurred more frequently in tumors treated with PDTC-ATO than those with ATO.

Conclusion

PDTC demonstrated the function to facilitate ATO against pancreatic cancer due to forming a stable complex to perturb ubiquitin-proteasome pathway.

A phase II study evaluating the role of bortezomib in the management of relapsed acute promyelocytic leukemia treated upfront with arsenic trioxide

The standard‐of‐care for patients with acute promyelocytic leukemia (APL) relapsing after upfront arsenic trioxide (ATO) therapy is not defined. The present study was undertaken to evaluate the safety of addition of bortezomib to ATO in the treatment of relapsed APL based on our previously reported preclinical data demonstrating synergy between these agents. This was an open label, nonrandomized, phase II, single‐center study. We enrolled 22 consecutive patients with relapsed APL. The median age was 26.5 years (interquartile range 17.5 to 41.5). The median time from initial diagnosis to relapse was 23.1 months (interquartile range 15.6 to 43.8). All patients achieved hematological remission at a median time of 45 days (range 40‐63). Nineteen patients were in molecular remission at the end of induction. Grade 3 adverse events occurred in eight instances with one patient requiring discontinuation of therapy for grade 3 neuropathy. Twelve (54.5%) patients underwent autologous transplantation (auto‐SCT) in molecular remission while the rest opted for maintenance therapy. The median follow‐up was 48 months (range 28‐56.3). Of the patients undergoing auto‐SCT, all except one was alive and relapse free at last follow‐up. Of the patients who opted for maintenance therapy, three developed a second relapse. For treatment of APL relapsing after upfront ATO therapy, addition of bortezomib to a standard ATO‐based salvage regimen is safe and effective. This trial was registered at http://www.clinicaltrials.gov as NCT01950611.

The Unfolded Protein Response: A Novel Therapeutic Target in Acute Leukemias

The unfolded protein response (UPR) is an evolutionarily conserved adaptive response triggered by the stress of the endoplasmic reticulum (ER) due, among other causes, to altered cell protein homeostasis (proteostasis). UPR is mediated by three main sensors, protein kinase RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor 6α (ATF6α), and inositol-requiring enzyme-1α (IRE1α). Given that proteostasis is frequently disregulated in cancer, UPR is emerging as a critical signaling network in controlling the survival, selection, and adaptation of a variety of neoplasias, including breast cancer, prostate cancer, colorectal cancer, and glioblastoma. Indeed, cancer cells can escape from the apoptotic pathways elicited by ER stress by switching UPR into a prosurvival mechanism instead of cell death. Although most of the studies on UPR focused on solid tumors, this intricate network plays a critical role in hematological malignancies, and especially in multiple myeloma (MM), where treatment with proteasome inhibitors induce the accumulation of unfolded proteins that severely perturb proteostasis, thereby leading to ER stress, and, eventually, to apoptosis. However, UPR is emerging as a key player also in acute leukemias, where recent evidence points to the likelihood that targeting UPR-driven prosurvival pathways could represent a novel therapeutic strategy. In this review, we focus on the oncogene-specific regulation of individual UPR signaling arms, and we provide an updated outline of the genetic, biochemical, and preclinical therapeutic findings that support UPR as a relevant, novel target in acute leukemias.

Combination Lenalidomide/Bortezomib Treatment Synergistically Induces Calpain-Dependent Ikaros Cleavage and Apoptosis in Myeloma Cells

Multiple myeloma had been successfully treated by combining lenalidomide and bortezomib with reports suggesting benefits of such a combination even in relapsed/refractory cases. Recently, it was demonstrated that Ikaros degradation by lenalidomide happens via proteasome-dependent pathway and this process is critical for the eradication of myeloma cells. On the basis of this, an antagonistic effect should be observed if a combination of both these agents were used, which however is not the observation seen in the clinical setting. Our study demonstrates that when these agents are combined they exhibit a synergistic activity against myeloma cells and degradation of Ikaros happens by a proteasome-independent calcium-induced calpain pathway. Our study identifies the crucial role of calcium-induced calpain pathway in inducing apoptosis of myeloma cells when this combination or lenalidomide and bortezomib is used. We also report that this combination enhanced the expression of CD38 compared with lenalidomide alone. Thus, data from our study would establish the rationale for the addition of daratumumab along with this combination to further enhance therapeutic activity against multiple myeloma. IMPLICATIONS: Lenalidomide and bortezomib combination degrades IKZF1 in multiple myeloma through a calcium-dependent calpain and caspase pathway. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/18/4/529/F1.large.jpg.

Resource utilization and cost effectiveness of treating acute promyelocytic leukaemia using generic arsenic trioxide

Arsenic trioxide (ATO)-based regimens are the standard of care for treating acute promyelocytic leukaemia (APL) and have replaced chemotherapy-based approaches. However, the cost of "patented" ATO is prohibitive because of patent rights. "Generic" ATO has been used in a few countries, but its implications for health resource utilization (HRU) and cost of treatment are unknown. We hypothesized that treating APL patients using generic ATO (APL-ATO) will be cost effective compared to the chemotherapy-based regimen (APL-CT). In a single-centre retrospective study, we used a bottom-up costing method to compare the direct medical cost of treatment and HRU between APL-ATO and APL-CT. These costs and the survival and relapse probabilities were imputed in a three-state Markov decision model to estimate the cost effectiveness of APL-ATO compared to APL-CT. The mean cost of treatment for APL-ATO (n = 30, $8500 ± 2078) was significantly less than for APL-CT (n = 30, $22 600 ± 5528) (P < 0·001). APL-ATO reduced hospitalization, antibiotic and antifungal usage (P < 0·001). In the Markov model, five-year treatment costs were significantly lower for APL-ATO ($11 131) than for APL-CT ($17 926) (P < 0·001). Treatment cost and health resource utilization were significantly lower for generic ATO-treated APL patients compared to the chemotherapy-based regimen.

Acute Promyelocytic Leukemia: Update on the Mechanisms of Leukemogenesis, Resistance and on Innovative Treatment Strategies

This review highlights new findings that have deepened our understanding of the mechanisms of leukemogenesis, therapy and resistance in acute promyelocytic leukemia (APL). Promyelocytic leukemia-retinoic acid receptor α (PML-RARa) sets the cellular landscape of acute promyelocytic leukemia (APL) by repressing the transcription of RARa target genes and disrupting PML-NBs. The RAR receptors control the homeostasis of tissue growth, modeling and regeneration, and PML-NBs are involved in self-renewal of normal and cancer stem cells, DNA damage response, senescence and stress response. The additional somatic mutations in APL mainly involve FLT3, WT1, NRAS, KRAS, ARID1B and ARID1A genes. The treatment outcomes in patients with newly diagnosed APL improved dramatically since the advent of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). ATRA activates the transcription of blocked genes and degrades PML-RARα, while ATO degrades PML-RARa by promoting apoptosis and has a pro-oxidant effect. The resistance to ATRA and ATO may derive from the mutations in the RARa ligand binding domain (LBD) and in the PML-B2 domain of PML-RARa, but such mutations cannot explain the majority of resistances experienced in the clinic, globally accounting for 5-10% of cases. Several studies are ongoing to unravel clonal evolution and resistance, suggesting the therapeutic potential of new retinoid molecules and combinatorial treatments of ATRA or ATO with different drugs acting through alternative mechanisms of action, which may lead to synergistic effects on growth control or the induction of apoptosis in APL cells.

Stromal cells downregulate miR-23a-5p to activate protective autophagy in acute myeloid leukemia

Complex molecular cross talk between stromal cells and the leukemic cells in bone marrow is known to contribute significantly towards drug-resistance. Here, we have identified the molecular events that lead to stromal cells mediated therapy-resistance in acute myeloid leukemia (AML). Our work demonstrates that stromal cells downregulate miR-23a-5p levels in leukemic cells to protect them from the chemotherapy induced apoptosis. Downregulation of miR-23a-5p in leukemic cells leads to upregulation of protective autophagy by targeting TLR2 expression. Further, autophagy inhibitors when used as adjuvants along with conventional drugs can improve drug sensitivity in vitro as well in vivo in a mouse model of leukemia. Our work also demonstrates that this mechanism of bone marrow stromal cell mediated regulation of miR-23a-5p levels and subsequent molecular events are relevant predominantly in myeloid leukemia. Our results illustrate the critical and dynamic role of the bone marrow microenvironment in modulating miRNA expression in leukemic cells which could contribute significantly to drug resistance and subsequent relapse, possibly through persistence of minimal residual disease in this environment.

A personalized approach to acute myeloid leukemia therapy: current options

Therapeutic options for acute myeloid leukemia (AML) have remained unchanged for nearly the past 5 decades, with cytarabine and anthracyclines and use of hypomethylating agents for less intensive therapy. Implementation of large-scale genomic studies in the past decade has unraveled the genetic landscape and molecular etiology of AML. The approval of several novel drugs for targeted therapy, including midostaurin, enasidenib, ivosidenib, gemtuzumab–ozogamicin, and CPX351 by the US Food and Drug Administration has widened the treatment options for clinicians treating AML. This review focuses on some of these novel therapies and other promising agents under development, along with key clinical trial findings in AML.

Autophagy: New Insights into Mechanisms of Action and Resistance of Treatment in Acute Promyelocytic leukemia

Autophagy is one of the main cellular catabolic pathways controlling a variety of physiological processes, including those involved in self-renewal, differentiation and death. While acute promyelocytic leukemia (APL) cells manifest low levels of expression of autophagy genes associated with reduced autophagy activity, the introduction of all-trans retinoid acid (ATRA)-a differentiating agent currently used in clinical settings-restores autophagy in these cells. ATRA-induced autophagy is involved in granulocytes differentiation through a mechanism that involves among others the degradation of the PML-RARα oncoprotein. Arsenic trioxide (ATO) is another anti-cancer agent that promotes autophagy-dependent clearance of promyelocytic leukemia retinoic acid receptor alpha gene (PML-RARα) in APL cells. Hence, enhancing autophagy may have therapeutic benefits in maturation-resistant APL cells. However, the role of autophagy in response to APL therapy is not so simple, because some autophagy proteins have been shown to play a pro-survival role upon ATRA and ATO treatment, and both agents can activate ETosis, a type of cell death mediated by the release of neutrophil extracellular traps (ETs). This review highlights recent findings on the impact of autophagy on the mechanisms of action of ATRA and ATO in APL cells. We also discuss the potential role of autophagy in the development of resistance to treatment, and of differentiation syndrome in APL.

Card9 as a critical regulator of tumor development

Caspase recruitment domain-containing protein 9 (Card9) is a myeloid cell-specific signaling protein that plays a critical role in NF-κB and MAPK activation. This leads to initiation of the inflammatory cytokine cascade, and elicits the host immune response against microbial invasion, especially in fungal infection. Current research indicates that Card9 plays an important role in tumor progression. Here, we review the data from preclinical and clinical studies of Card9 and suggest the potential for Card9-targeted interventions in the prevention or treatment of certain tumors.

Therapeutic Modulation of Autophagy in Leukaemia and Lymphoma

Haematopoiesis is a tightly orchestrated process where a pool of hematopoietic stem and progenitor cells (HSPCs) with high self-renewal potential can give rise to both lymphoid and myeloid lineages. The HSPCs pool is reduced with ageing resulting in few HSPC clones maintaining haematopoiesis thereby reducing blood cell diversity, a phenomenon called clonal haematopoiesis. Clonal expansion of HSPCs carrying specific genetic mutations leads to increased risk for haematological malignancies. Therefore, it comes as no surprise that hematopoietic tumours develop in higher frequency in elderly people. Unfortunately, elderly patients with leukaemia or lymphoma still have an unsatisfactory prognosis compared to younger ones highlighting the need to develop more efficient therapies for this group of patients. Growing evidence indicates that macroautophagy (hereafter referred to as autophagy) is essential for health and longevity. This review is focusing on the role of autophagy in normal haematopoiesis as well as in leukaemia and lymphoma development. Attenuated autophagy may support early hematopoietic neoplasia whereas activation of autophagy in later stages of tumour development and in response to a variety of therapies rather triggers a pro-tumoral response. Novel insights into the role of autophagy in haematopoiesis will be discussed in light of designing new autophagy modulating therapies in hematopoietic cancers.

Arsenic trioxide promoting ETosis in acute promyelocytic leukemia through mTOR-regulated autophagy

Despite the high efficacy and safety of arsenic trioxide (ATO) in treating acute promyelocytic leukemia (APL) and eradicating APL leukemia-initiating cells (LICs), the mechanism underlying its selective cytotoxicity remains elusive. We have recently demonstrated that APL cells undergo a novel cell death program, termed ETosis, through autophagy. However, the role of ETosis in ATO-induced APL LIC eradication remains unclear. For this study, we evaluated the effects of ATO on ETosis and the contributions of drug-induced ETosis to APL LIC eradication. In NB4 cells, ATO primarily increased ETosis at moderate concentrations (0.5–0.75 μM) and stimulated apoptosis at higher doses (1.0–2.0 μM). Furthermore, ATO induced ETosis through mammalian target of rapamycin (mTOR)-dependent autophagy, which was partially regulated by reactive oxygen species. Additionally, rapamycin-enhanced ATO-induced ETosis in NB4 cells and APL cells from newly diagnosed and relapsed patients. In contrast, rapamycin had no effect on apoptosis in these cells. We also noted that PML/RARA oncoprotein was effectively cleared with this combination. Intriguingly, activation of autophagy with rapamycin-enhanced APL LIC eradication clearance by ATO in vitro and in a xenograft APL model, while inhibition of autophagy spared clonogenic cells. Our current results show that ATO exerts antileukemic effects at least partially through ETosis and targets LICs primarily through ETosis. Addition of drugs that target the ETotic pathway could be a promising therapeutic strategy to further eradicate LICs and reduce relapse.

(-)-Epicatechin rescues the As2 O3 -induced HERG K+ channel deficiency possibly through upregulating transcription factor SP1 expression

(-)-Epicatechin (EPI) has beneficial effects on the cardiovascular disease. The human ether-a-go-go-related gene (HERG) potassium channel is crucial for repolarization of cardiac action potential. Dysfunction of the HERG channel can cause long QT syndrome type 2 (LQT2). Arsenic trioxide (As2 O3 ) has shown efficacy in the treatment of acute promyelocytic leukemia. However, As2 O3 can induce the deficiency of HERG channel and cause LQT2. In this study, we examined whether EPI could rescue the As2 O3 -induced HERG channel deficiency. We found that 3 μM EPI obviously increased protein expression and current of HERG channel. EPI was able to recover the protein expression and current of HERG channel disrupted by As2 O3 . EPI was able to increase the expression of SP1 protein and recover the expression of SP1 protein disrupted by As2 O3 . In addition, EPI significantly shortened action potential duration prolonged by As2 O3 . Our data suggest that EPI rescues As2 O3 -induced HERG channel deficiency through upregulating SP1 expression.

Retinoic acid and arsenic trioxide sensitize acute promyelocytic leukemia cells to ER stress

Retinoic acid (RA) in association with chemotherapy or with arsenic trioxide (ATO) results in high cure rates of acute promyelocytic leukemia (APL). We show that RA-induced differentiation of human leukemic cell lines and primary blasts dramatically increases their sensitivity to endoplasmic reticulum (ER) stress-inducing drugs at doses that are not toxic in the absence of RA. In addition, we demonstrate that the PERK pathway, triggered in response to ER stress, has a major protective role. Moreover, low amounts of pharmacologically induced ER stress are sufficient to strongly increase ATO toxicity. Indeed, in the presence of ER stress, ATO efficiently induced apoptosis in RA-sensitive and RA-resistant APL cell lines, at doses ineffective in the absence of ER stress. Our findings identify the ER stress-related pathways as potential targets in the search for novel therapeutic strategies in AML.

Current first- and second-line treatment options in acute promyelocytic leukemia

Outcome of acute promyelocytic leukemia (APL) has remarkably improved during the last 30 years, especially after the identification of PML-RARA oncogene as a key in the pathogenesis of APL and all-trans retinoic acid as therapeutic agent. Arsenic trioxide has been recently demonstrated to be the most effective single antileukemic agent and it has also showed synergistic action when combined with all-trans retinoic acid, decreasing relapse rate especially in low/intermediate-risk settings. Therapeutic advances led to complete remission rates of more than 90%, modifying disease history. In relapse setting, arsenic trioxide-based regimens showed efficacy for the achievement of second molecular complete remission. The most challenging issue in APL management remains the significant early deaths rate, nowadays the principal reason for treatment failure.